Concentration and Physicochemical Properties of Chitosan Derivatives Determine the Induction of Defense Responses in Roots and Leaves of Tobacco (Nicotiana tabacum) Plants

Problem statement: The chitosan derivatives promote diverse defensive responses in plants, which are affected by chitosan chemical features and concentration. Glucanase (EC 3.2.1.6), Phenylalanine Ammonia-Lyase (PAL, EC 4.3.1.5) and peroxidase (POD, EC 1.11.1.6) are key enzymes in tobacco defense responses. Thus, the aim of this study was to know the behavior of their enzymatic activity in leaves and roots of whole tobacco plants, previously elicited with chitosan derivatives of different molecular weight and acetylating degree. Approach: 25 day-old tobacco plants were treated with three chitosan derivatives (CH- 63, CH-88 and OLG) of different chemical features. True leaves and roots were sampled after three, six, nine and 12 days post-treatment for further evaluation of the enzymatic activities. Results: Chitosan treatments increased the activity of all three studied enzymes depending on the concentration and chemical feature of the derivative. The highest enzymatic activities with polymers occurred at 1 g L^-1 while the oligochitosan mixture achieved good enzymatic levels as compared to controls from 0.1 g L^-1 onwards. The Degree of Acetylation (DA) affected PAL activity; a more acetylated polymer induced a higher activity than a less acetylated one. However, the low levels of acetylation favored POD activity. The systemic induction of enzymatic activities was detected in leaves of treated plants after root application. The effect of the acetylation degree was systemically transmitted to the leaves by POD, but not by PAL activity; so the transmission of the acetylating degree influence beyond the tissue directly elicited by chitosan polymer depended on each enzymatic response tested. Conclusion: This study proved that various chitosan derivatives induced and raised lasting β-1,3-glucanase, PAL and POD activities in tobacco leaves and roots as local or systemic responses, which could lead to the accumulation of secondary metabolites and formation of barriers that all together enhance plant resistance against pathogens.